Method for Collecting Uranium by Treatment Process of Washing Waste Liquid Generated in Uranium Hexafluoride Cylinder Washing Process

ABSTRACT

Disclosed are a method and a device for recovering uranium (U) using a process for chemically treating washing wastewater of a uranium hexafluoride (UF6) cylinder. The method and the device are provided to separate uranium (U) from the wastewater released during a process of washing the uranium hexafluoride (UF6) cylinder and to release a filtrate that satisfies atomic energy licensing standards and environmental regulation standards using evaporation and condensation. Accordingly, an independent technology and process for treating the wastewater released during the process of washing the uranium hexafluoride (UF6) cylinder are ensured, which provides easier maintenance and greatly reduces costs compared to the purchase and operation of apparatuses manufactured by foreign makers.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application is a continuation of PCT Application NoPCT/KR2016/013505, filed Nov. 23, 2016, which claims priority to KoreanPatent Application No. 10-2016-0052523, filed Apr. 28, 2016, the entireteachings and disclosure of which are incorporated herein by referencethereto.

TECHNICAL FIELD

The present invention relates to a method and a device for recoveringuranium using a process for chemically treating washing wastewater froma uranium hexafluoride (UF₆) cylinder. More particularly, the presentinvention relates to a method and a device that precipitate sodiumdiuranate (NaDU) and sodium fluoride (NaF) solids from washingwastewater from a uranium hexafluoride (UF₆) cylinder to recover uranium(U), which is a radioactive element, and fluorine (F), which is a toxicelement, and that releases a filtrate satisfying atomic energy licensingstandards and environmental regulation standards, thereby minimizing theamount of waste that is released.

BACKGROUND ART

Cylinder washing wastewater, which is a reactant used in the presentinvention, is released during the following process.

Demineralized water is used as washing water, a mixed solution including10% hydrogen peroxide (H₂O₂) and 90% sodium carbonate (Na₂CO₃) is usedas a washing solution, and a 30B-type cylinder used in Korea isgenerally washed five times per cylinder in a way that the cylinder iswashed twice using washing water and three times using the washingsolution shown in Table 1. The wastewater is released in an amount of 20Liters for each washing, and the total amount of wastewater that isreleased is about 100 Liters. The wastewater is radioactive waste matterthat is inevitably released during the production of atomic energy fuel,and it is an object of the present invention to treat the radioactivewaste matter using an effective method, thereby minimizing the amount ofsuch radioactive waste matter.

TABLE 1 Details of the process of washing the cylinder Wash WashingAddition Number solution amount Washing time and cylinder angle 1Demi-Water 20 Liters 15 min/90° 15 min/69° 15 min/90° 2 Na₂CO₃/H₂O₂ 20Liters 15 min/90° 15 min/69° 15 min/90° 3 Na₂CO₃/H₂O₂ 20 Liters 15min/90° 15 min/69° 15 min/90° 4 Demi-Water or 20 Liters 15 min/90° 15min/69° 15 min/90° Na₂CO₃/H₂O₂ 5 Demi-Water 20 Liters 15 min/90° 15min/69° 15 min/90° Total (washing of one cylinder) 100 Liters  Total3.75 hr

A conventional process for chemically treating cylinder washingwastewater includes a process of precipitating ammonium diuranate (ADU)and a process of precipitating sodium diuranate (NaDU), and mostprocesses suggested by foreign makers include a sodium diuranate (NaDU)process. This is because, during the sodium diuranate (NaDU) process,sodium hydroxide (NaOH), which is easily handled, is used, the amountsof uranium (U) and fluorine (F) easily satisfy regulation values, andthe radioactive waste matter is released in a small amount.

In Korea, wastewater has been treated using the conventional ADU process(FIG. 1a ). However, since the process does not satisfy atomic energylicensing standards and environmental regulation standards, secondarywastewater released during the ADU precipitation process is treatedusing pyrolysis to satisfy the atomic energy licensing standards andenvironmental regulation standards, and is then released to theatmosphere. However, the pyrolysis process has significant drawbacks inthat the number of process control factors is large and maintenancecosts are high. Accordingly, a novel process needs to be developed sothat wastewater can be directly released to the environment without thepyrolysis process.

In overseas processes, a process for treating the washing wastewater ofthe uranium (UF₆) cylinder using NaDU precipitation (FIG. 1b ) has beenused, and details of the process are as follows. Nitric acid (HNO₃) isinjected into the wastewater [demineralized water and hydrogen peroxide(H₂O₂)+sodium carbonate (Na₂CO₃)], which is collected in a first storagetank (column tank) to dissolve impurities, and the solution is thenrecycled and heated to remove CO₂ and perform uniform mixing. Theresultant mixture is transported to a second storage tank (decay tank).After the radioactivity of the transported wastewater decreases in thestorage tank (decay tank), the wastewater is transported to aprecipitator in order to perform the process of precipitating sodiumdiuranate (NaDU). About 33 wt % of a sodium hydroxide (NaOH) aqueoussolution is slowly injected into the wastewater, which is transported tothe precipitator and is agitated using an agitator at a temperature of40 to 60° C. under a condition of a pH of 9 to 11. Uranium contained inthe wastewater is precipitated in a sodium diuranate (NaDU) form, andthe concentration of uranium (U) in the supernatant is 100 ppm or less.Subsequently, the supernatant is evaporated in an evaporator, and theprecipitate is obtained by filtration in a filter press. Most of thewastewater is evaporated during an evaporation process, and the moisturecontent of the remaining sludge is about 30%. The sludge is heated to55° C. in a vacuum to be dried so that the moisture content is 1% orless. Subsequently, the dried sludge is discarded while contained in adrum. The released moisture is collected in a condensate storage tankthrough a condenser. When the condensate storage tank is fully filled,sampling and measurement are performed, and the condensed water isreleased if a release condition is satisfied. The release condition isthat the concentration of the alpha radioactivity is 1 ppm or less onaverage, that is, 100 kBq/m³ or less.

The present inventors have developed a process including [sodiumdiuranate (NaDU) precipitation→evaporation→condensation] (FIG. 1c )using an independent apparatus in order to solve the problem whereby theconventional ADU process does not satisfy atomic energy licensingstandards and environmental regulation standards and to simplify theconventional Korean process (ADU) and the overseas process (NaDU),thereby accomplishing the present invention.

Korean Patent Application Publication No. 10-2009-0112862 (Laid-opendate: Oct. 29, 2009) describes aspects of the foregoing discussion.

BRIEF SUMMARY

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the related art, and an object of thepresent invention is to provide (1) a method of separating uranium (U)from wastewater released during a process of washing a uraniumhexafluoride (UF₆) cylinder and of releasing a filtrate satisfyingatomic energy licensing standards and environmental regulationstandards; and (2) a device for controlling the pH of the washingwastewater of the cylinder using sodium hydroxide (NaOH) to separateuranium (U) via precipitation in a sodium diuranate (NaDU) form and thenevaporating the filtrate so that uranium (U) remaining in the filtrateis further separated and moisture is condensed for release.

In order to accomplish the above object, the present invention providesa method of recovering uranium using a process for chemically treatingwashing wastewater (hydrogen peroxide (H₂O₂)+sodium carbonate (Na₂CO₃)+auranium complex) released during a process of washing a uraniumhexafluoride (UF₆) cylinder. The method includes (1) adding sodiumhydroxide (NaOH) to the washing wastewater to precipitate the uraniumcomplex, contained in the washing wastewater, in a sodium diuranate(NaDU) solid form, (2) separating a sodium diuranate (NaDU) precipitate,formed during the step (1), from the wastewater using filtration, (3)evaporating the wastewater filtered during the step (2), (4) filteringthe wastewater remaining after the evaporating of the step (3), (5)evaporating the wastewater filtered during the step (4), and (6) coolinga vapor generated during the steps (3) and (5) to recover a condensateand then checking the amounts of uranium (U) and fluorine (F) thatremain.

Demineralized water or a mixed solution including the hydrogen peroxide(H₂O₂) and the sodium carbonate (Na₂CO₃) is used as a washing solutionduring the process of washing the uranium hexafluoride (UF₆) cylinder,resulting in the generation of washing wastewater.

A sodium hydroxide (NaOH) aqueous solution is added while the washingwastewater is heated to a predetermined temperature during the step (1),thereby precipitating uranium from the wastewater in a sodium diuranate(NaDU) form.

Steam is supplied to an evaporator to evaporate the wastewater duringthe steps (3) and (5).

The present invention also provides a device for recovering uraniumusing a process for chemically treating washing wastewater of a uraniumhexafluoride (UF₆) cylinder. The device includes a NaDU reactor 1 foradding sodium hydroxide (NaOH) to the washing wastewater (hydrogenperoxide (H₂O₂)+sodium carbonate (Na₂CO₃)+a uranium complex), releasedduring the process of washing the uranium hexafluoride (UF₆) cylinder,to thus precipitate uranium from the wastewater in a sodium diuranate(NaDU) form, a filter separator 2 connected to the NaDU reactor 1 toseparate a sodium diuranate (NaDU) precipitate generated in the NaDUreactor 1 and a filtrate, a filtrate reception tank 3 connected to thefilter separator 2 to store the filtrate separated using the filterseparator 2, an evaporator 4 connected to the filtrate reception tank 3to evaporate the filtrate supplied from the filtrate reception tank 3, aheat exchanger 5 connected to the evaporator 4 to cool vapor obtainedduring evaporation using the evaporator 4, thus condensing the vapor,and a condensate storage tank 6 connected to the heat exchanger 5 tostore a condensate.

Another filter separator 2′ is connected to the evaporator 4 to filterthe wastewater remaining after sodium diuranate (NaDU) is evaporated,thereby separating the precipitate and the filtrate.

The condensate storage tank 6 includes a first condensate storage tank6-1, for storing the condensate to be released after the amounts ofuranium (U) and fluorine (F) are checked, and a second condensatestorage tank 6-2, for storing the condensate that is to be chemicallytreated.

Provided are a method and a device that separate uranium (U) fromwastewater released during a process of washing a uranium hexafluoride(UF₆) cylinder using precipitation and that release a filtratesatisfying atomic energy licensing standards and environmentalregulation standards using evaporation and condensing. Accordingly, anindependent technology and process for treating the washing wastewaterof the uranium hexafluoride (UF₆) cylinder are ensured, thus improvingmaintenance and processability, contributing to ensuring sourcetechnologies, improving the technical skill of the national atomicenergy industry, and creating a new industrial growth engine usingoverseas business connections.

Further, costs may be significantly reduced compared to the purchase andoperation of process technologies and apparatuses provided by foreignmakers.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1a showing a conventional process of precipitating ammoniumdiuranate (ADU);

FIG. 1b showing a conventional process of precipitating sodium diuranate(NaDU);

FIG. 1c showing a process of precipitating sodium diuranate (NaDU)according to the present invention;

FIG. 2 shows a device for recovering uranium (U) using a process fortreating washing wastewater released during a process of washing auranium hexafluoride (UF₆) cylinder in the related art (foreignprocess);

FIG. 3 shows a device for recovering uranium (U) using a process fortreating washing wastewater released during a process of washing auranium hexafluoride (UF₆) cylinder according to the present invention;and

FIG. 4 schematically shows the experimental apparatus of 5 inExperimental Examples 1 to 5.

DETAILED DESCRIPTION

Hereinafter, the present invention will be described in detail.

The present invention provides a method of recovering uranium (U) usinga process for treating washing wastewater (hydrogen peroxide(H₂O₂)+sodium carbonate (Na₂CO₃)+a uranium complex) released during aprocess of washing a uranium hexafluoride (UF₆) cylinder. The methodincludes (1) adding sodium hydroxide (NaOH) to the washing wastewater toprecipitate the uranium complex, contained in the washing wastewater, ina sodium diuranate (NaDU) form, (2) separating a sodium diuranate (NaDU)precipitate formed during the step (1) and the washing wastewater usingfiltration, (3) evaporating the washing wastewater filtered during thestep (2), and (4) cooling vapor generated during the step (3) to recovera condensate and then checking the remaining amounts of uranium (U) andfluorine (F).

Meanwhile, as for the process of washing the uranium hexafluoride (UF₆)cylinder, conventionally, a separate chemical treatment process [theprocess of precipitating sodium fluoride (NaF)→the wastewater pyrolysisprocess] must be performed after the precipitation reaction of sodiumdiuranate (NaDU) using an ADU process in order to satisfy atomic energylicensing standards and environmental regulation standards. A processsuggested by foreign makers necessarily includes injecting a nitric acid(HNO₃) into a first wastewater storage tank (column tank) to thus removeimpurities. However, the present invention requires neither a separateprocess for chemically treating the washing wastewater released duringthe process of washing the uranium hexafluoride (UF₆) cylinder nor aprocess for injecting nitric acid (HNO₃) into the washing wastewater,but treats the washing wastewater using an independent apparatus.

The method of recovering uranium according to the present invention mayinclude, after the step (3), (5) filtering and evaporating thewastewater remaining after the evaporating of the step (3), and (6)heat-exchanging the vapor generated during the step (5) to recover acondensate and then checking the amounts of uranium (U) and fluorine (F)that remain.

A demineralized water or a mixed solution, including hydrogen peroxide(H₂O₂) and sodium carbonate (Na₂CO₃), is used as a washing solutionduring the process of washing the uranium hexafluoride (UF₆) cylinder,causing generation of the washing wastewater. When the mixed solutionincluding hydrogen peroxide (H₂O₂) and sodium carbonate (Na₂CO₃) isused, it is preferable that 10 wt % of hydrogen peroxide (H₂O₂) and 90wt % of sodium carbonate (Na₂CO₃) be mixed.

During the evaporation of the filtered washing wastewater, steam issupplied to evaporate water, the evaporated water is transported througha heat exchanger to a condensate storage tank, and a residue is recycledto filter the remaining sodium diuranate (NaDU) solid and washingwastewater and then evaporate the filtered washing wastewater. Thisprocedure may be repeated.

Preferably, the demineralized water and the mixed solution includinghydrogen peroxide (H₂O₂) and sodium carbonate (Na₂CO₃) are used duringwashing of the cylinder to convert remaining tetravalent uranium (U⁴⁺:insoluble) into hexavalent uranium (U⁶⁺: water-soluble). The washingwastewater of the cylinder includes a 0.1 to 3.0M uranyl nitrate aqueoussolution [UO₂(NO₃)₂.6H₂O], and about 90% of the washing wastewater iswater. The concentration of uranium (U) is 1.0 kg-UF₆/100 l, and a 30Btype is used as the cylinder.

Further, the method may include a step of preparing for washing and awashing step. The heel of the inside of the uranium hexafluoride (UF₆)cylinder used during the process of washing the cylinder is 3 kg orless, and a radiation dose rate is 50 μ/hr or less at a position that is10 cm above the external surface of the cylinder. During the washingstep, a nozzle is inserted into the cylinder and washing water (20 L ofdemineralized water or 20 L of a mixed washing solution includinghydrogen peroxide (H₂O₂) and sodium carbonate (Na₂CO₃)) is sprayedthrough the nozzle (the cylinder is washed while being verticallydisposed at 90° C., 69° C., and 90° C. sequentially, and is washed usingthe demineralized water once, the washing solution twice, and thedemineralized water twice, and if necessary, washing is performed twomore times using the aqueous solution including hydrogen peroxide (H₂O₂)and sodium carbonate (Na₂CO₃)).

Further, the present invention provides a device for recovering uraniumusing a process for treating the washing wastewater that is releasedduring a process of washing a UF₆ cylinder. The device includes a NaDUreactor 1 for adding sodium hydroxide (NaOH) to the washing wastewater(hydrogen peroxide (H₂O₂)+sodium carbonate (Na₂CO₃)+a uranium complex),released during the process of washing the uranium hexafluoride (UF₆)cylinder, to thus precipitate a sodium diuranate (NaDU) solid, a filterseparator 2 connected to the NaDU reactor 1 to separate the sodiumdiuranate (NaDU) solid generated in the NaDU reactor 1 and a filtrate, afiltrate reception tank 3 connected to the filter separator 2 to storethe filtrate separated using the filter separator 2, an evaporationvessel 4 connected to the filtrate reception tank 3 to evaporate thefiltrate supplied from the filtrate reception tank 3, a filter separator2′ for filtering the wastewater remaining after evaporation to recyclethe filtered wastewater to the evaporation vessel 4, a heat exchanger 5connected to the evaporation vessel 4 to cool vapor obtained duringevaporation using the evaporation vessel 4, thus condensing the vapor,and a condensate storage tank 6 connected to the heat exchanger 5 tostore condensate.

The filter separator 2′ may be connected to the evaporation vessel 4 toseparate the sodium diuranate (NaDU) solid and the filtrate, therebyachieving two-stage filtration using the two filter separators.

The condensate storage tank 6 may include a first condensate storagetank 6-1, for storing the condensate to be released after the amounts ofuranium (U) and fluorine (F) are checked, and a second condensatestorage tank 6-2, for storing the condensate that is to be chemicallytreated.

Comparing the recovering device of the present invention, shown in FIG.3, with the conventional device for treating washing wastewater shown inFIG. 2, the NaDU reactor of the present invention includes threeconstitutional elements of the conventional device, that is, a firstwastewater storage tank (column tank), a second wastewater storage tank(decay tank), and a precipitation reactor. In the present invention, twofilter separators 2 and 2′ may be provided, thereby improving thequality of the uranium (U) that is recovered.

A better understanding of the present invention may be obtained throughthe following Examples. It will be obvious to those skilled in the artthat the Examples are set forth to illustrate the present invention butare not to be construed to limit the scope of the present invention.

Example 1. Reaction Mechanism During Washing of UF₆ Cylinder

(1) Reaction During Washing of UF₆ Cylinder

UF₆+2H₂O→UO₂F₂+4HF

UF₄+2H₂O₂+Na₂CO₃→UO₂F₂+2H₂O+2NaF+½O_(2↑)+CO_(2↑)

Na₂CO₃+2HF→2NaF+H₂O+CO_(2↑)

Example 2. Reaction Mechanism of Precipitation of Uranium

(1) Case where nitric acid (HNO₃) is added to the washing solution andammonia (NH₃) is added thereto to precipitate ammonium diuranate (ADU)

2UO₂(NO₃)₂+3H₂O+6NH₃→(NH₄)₂U₂O₇+4NH₄NO₃  1)

HF+NH₃→NH₄F  2)

HNO₃+NH₃→NH₄NO₃  3)

(2) Case where Sodium Hydroxide (NaOH) is Added to the Washing Solutionto Precipitate Sodium Diuranate (NaDU)

2UO₂F₂+6NaOH→Na₂U₂O₇+4NaF+3H₂O

Meanwhile, the composition of the washing solution was analyzed inconsideration of the aforementioned reaction mechanisms, and the resultsare shown in Table 2 below.

TABLE 2 Composition table of washing solution (kg per one cylinder (%))Composition CASE I CASE II-1 CASE II-2 CASE III-1 CASE III-2 CASE III-3CASE III-4 H₂O 96.22 101.844 96.812 101.79 104.313 103.773 109.473(95.53) (90.36) (96.35) (81.4) (90.37) (89.81) (90.06) Na₂CO₃ 3.487 —0.307 — 0.307 3.487 3.487 (3.47) (0.30) (0.27) (3.02) (2.87) UO₂F₂ 0.609— 0.609 — — — (0.61) (0.61) Na₂U₂O₇ — — — — 0.627 0.627 0.627 (0.54)(0.54) (0.52) UO₂(NO₃)₂ — 0.779 — — — (0.69) ADU — — — 0.617 — (0.49)NaF 0.232 0.232 2.752 0.232 2.918 0.398 6.698 (0.23) (0.21) (2.74)(0.18) (2.53) (0.34) (5.51) NaOH — — — — 7.263 7.263 1.263 (6.29) (6.29)(1.04) HF — 0.079 — — — — (0.07) NH₄F — — — 0.263 — — (0.21) NH₄NO₃ — —— 16.559 — — (13.24) NaNO₃ — 5.592 — 5.592 — — (4.96) (4.47) HNO₃ —4.174 — — — — (3.70) Total 100.55 112.7 100.428 125.054 115.428 115.548121.548 (100) (100) (100) (100) (100) (100) (100)

1. CASE I: Crude liquid immediately after washing 2. CASE II-1: Nitricacid is added to washing crude liquid (based on 10N concentration, 10 L− 15.6 kg) CASE II-2: Hydrofluoric acid is added to washing crude liquid(based on 50% concentration, 2 L − 2.4 kg) 3. CASE III-1: NH3 is addedto CASE II-1 solution (only amount suitable for neutralization isconsidered) CASE III-2: 50% NaOH is added to CASE II-2 solution (basedon 10 L − 15 kg) CASE III-3: 50% NaOH is added to CASE I (10 L − 15 kg)CASE III-4: Hydrofluoric acid is added to CASE III-3 solution (based on5 L − 6 kg)

4. Decomposition of Na₂CO₃ in aqueous solution and removal of CO₂ byheating were not considered

The following Experimental Examples are provided in order to compare andanalyze precipitation tests of ammonium diuranate (ADU) and sodiumdiuranate (NaDU), performed in the course of developing the process ofthe present invention, thereby selecting the optimum process. As aresult, a sodium diuranate (NaDU) precipitation process was found to beuseful in satisfying atomic energy licensing standards and environmentalregulation standards. Further, in order to further analyze the result ofprecipitation of sodium diuranate (NaDU), the precipitation of sodiumhydroxide (NaOH) and ammonium fluoride (NH₄F) was compared.

Experimental Example 1. Results of Comparative Precipitation Tests ofAmmonium Diuranate (ADU)/Sodium Diuranate (NaDU)

TABLE 3 (1) Test for precipitation of calcium fluoride (CaF2) afterprecipitation of ammonium diuranate (ADU) U F Order Test process (ppm //Bq/cc) (ppm) Note 1st ADU-precipitation 29.3 // 3.2 38 supernatant +slaked lime 2nd ADU-precipitation 5.40 // 0.6 66 supernatant + slakedlime * Regulation value: Activity (alpha, beta) <0.08 Bq/cc, fluorine(F) <10 ppm * ppm is converted into Bq/cc in consideration of specificradioactivity of 5% U-235

TABLE 4 (2) Test for precipitation of sodium fluoride (NaF) afterprecipitation of sodium diuranate (NaDU) U F Order Test process (Bq/cc)(ppm) Note 1st NaDU-precipitation 0.006 1 supernatant + NH₄F 2ndNaDU-precipitation 0.011 1 supernatant + NH₄F

As seen from the result of the precipitation tests on ammonium diuranate(ADU) and sodium diuranate (NaDU), with respect to the removal ofuranium (U), the ammonium diuranate (ADU) treatment is found not tosatisfy the regulatory value for the content of uranium (U). The sodiumdiuranate (NaDU) precipitation reaction is simpler and has a shorterreaction time, compared to the precipitation reaction of ammoniumdiuranate (ADU), thus ensuring high economic feasibility. Further, withrespect to the removal of fluorine (F), since nitric acid (HNO₃) andammonia (NH₃) must be used during the treatment of ammonium diuranate(ADU), calcium fluoride (CaF₂) is essentially precipitated, and it isdifficult to satisfy environmental regulation values governing thecontent of fluorine (F). However, when a process of precipitating sodiumfluoride (NaF) is used, sodium fluoride (NaF) can be treated during theprocess.

Further, when the precipitation of sodium diuranate (NaDU) and sodiumfluoride (NaF) is used, the reagent required during the process (nitricacid (HNO₃), ammonia (NH₃), or calcium hydroxide (Ca(OH)₂)) may bereplaced with sodium hydroxide (NaOH) or ammonium fluoride (NH₄F), whichmay be easily handled, thereby removing harmful factors during handlingand reducing costs.

Accordingly, it can be seen that when the precipitation of sodiumdiuranate (NaDU) and sodium fluoride (NaF) is used to treat the washingwastewater of the uranium hexafluoride (UF₆) cylinder, there are meritsin terms of the convenience of the process, the economic feasibility ofthe process, and a reduction in secondary waste.

Experimental Example 2. Precipitation Test of Ammonium Diuranate (ADU)

TABLE 5 (1) First test U F Order Test process (ppm) (ppm) Note 1st Crudeliquid (500 cc) + 7.0 2,800 Crude liquid filtration + nitric acid isused after (40 cc) + NH₃ being filtered 2nd Crude liquid (500 cc) + 3.32,300 nitric acid (100 cc) + NH₃ 3rd Crude liquid (500 cc) + 2.2 2,500nitric acid (50 cc) + NH₃

TABLE 6 (2) Second test U F Order Test process (ppm) (ppm) 1st Washingcrude liquid 9,272 2,800 2nd Crude liquid (600 cc) + 17.8 2,400 nitricacid (60 cc) + NH₃ 3rd Crude liquid (500 cc) + 1,122 2,400 nitric acid(50 cc) + NH₃ 4th Supernatant of the third 29.3 38 process of the secondtest + slaked lime 5th Supernatant of the second 5.4 66 process of thesecond test + slaked lime 6th Supernatant of the third 1,054 2,800process of the first test 7th Crude liquid + ( ) 10% 216 2,500

The precipitation of ammonium diuranate (ADU) using nitric acid (HNO₃)treatment has drawbacks in that the reaction conditions are verysensitive, the reaction time is very long, and fluorine (F) contained inthe filtrate cannot be treated. Further, if filtration is not performedimmediately after precipitation, uranium (U) is eluted back into asupernatant, thus increasing the concentration of uranium (U).

Experimental Example 3. Sodium Diuranate (NaDU) Precipitation Test

TABLE 7 (1) First test U F Order Test process (ppm) (ppm) 1st Crudeliquid + NaOH + hydrofluoric 13.9 2,400 acid + precipitation 2nd Crudeliquid + heating + NaOH + 2.1 2,500 hydrofluoric acid + precipitation3rd Crude liquid + nitric acid + NaOH + 59.4 2,500 hydrofluoric acid +precipitation

TABLE 8 (2) Second test U F Order Test process (ppm) (ppm) Note 1st 300cc of crude 6.1 2,500 Na₂CO₃ is used liquid→Na₂CO₃ before precipitation(19.5 g)→agitation→ (heated) heating to 74° C.→ 45 cc of NaOH→coagulant→filtration 2nd 300 cc of crude 17.1 10,000 Na₂CO₃ is usedliquid→Na₂CO₃(19.5 before precipitation g)→agitation→ Hydrofluoric acidHF (pH₄)→heating to is added after 60° C.→45 cc precipitation (heated)of NaOH→ coagulant→filtration

TABLE 9 (3) Third test U F Order Test process (ppm) (ppm) Note 1st 300cc of crude 10.6 1,500 No hydrofluoric liquid→heating acid is used to75° C.→45 cc (heated) of NaOH→cooling→ coagulant→filtration 2nd 300 ccof crude 10.1 11,200 Hydrofluoric acid liquid→heating to is used after75° C.→45 cc of precipitation NaOH→40 cc of (heated) HF→cooling→coagulant→filtration 3rd 300 cc of crude 10.6 1,900 No hydrofluoricliquid→heating to acid is used 75° C.→30 cc of (heated) NaOH→cooling→coagulant→filtration 4th 300 cc of crude 11.0 12,600 Hydrofluoric acidliquid→heating to is used after 75° C.→30 cc of precipitation NaOH→40 ccof (heated) HF→cooling→ coagulant→filtration

Special feature: In all four cases, flocculation using Floc ispreferably not performed, and the supernatant is not transparent beforefiltration

TABLE 10 (4) Fourth test U F Order Test process (ppm) (ppm) Note 1st 300cc of crude 13.9 10,500 Hydrofluoric acid liquid→6 cc of is used beforeHF→heating to precipitation 75° C.→15 cc of (heating) NaOH→cooling to35° C.→coagulant→ filtration 2nd 300 cc of crude 22.8 11,200Hydrofluoric acid liquid→6 cc of is used before HF→15 cc ofprecipitation NaOH→cooling to (unheated) 35° C.→coagulant→ filtration

Special feature: In both cases, flocculation using Floc is preferablyperformed

TABLE 11 (5) Fifth test U F Order Test process (ppm) (ppm) Note 1st 300cc of crude 25.2 11,100 NH₄F is used before liquid→9 cc of precipitationNH₄F→heating to (heated) 75° C.→15 cc of NaOH→cooling→coagulant→filtration 2nd 300 cc of crude 4.3 14,500 NH₄F is used beforeliquid→9 cc of precipitation NH₄F→15 cc of (unheated) NaOH→cooling→coagulant→filtration

Special feature: In all four cases, flocculation using Floc ispreferably performed, but the supernatant is not transparent beforefiltration

TABLE 12 (6) Sixth test U F Order Test process (ppm) (ppm) Note 1st 300cc of crude 9.1 1,900 No hydrofluoric liquid→heating to acid is used 75°C.→15 cc of (heated) NaOH→cooling→ coagulant→filtration 2nd Ditto 13.41,800 Ditto

Special feature: In all four cases, flocculation using Floc ispreferably not performed, and the supernatant is not transparent beforefiltration

Experimental Example 4. Precipitation Test of Fluorine (F)

TABLE 13 (1) Precipitation test of calcium fluoride (CaF2) afterprecipitation of ammonium diuranate (ADU) U F Order Test process (ppm //Bq/cc) (ppm) 1st ADU-precipitation 29.3 // 3.2 38 supernatant + slakedlime 2nd ADU-precipitation 5.40 // 0.6 66 supernatant + slaked lime

Regulation value: Activity (alpha, beta)<0.08 Bq/cc, fluorine (F)<10 ppm

ppm is converted into Bq/cc in consideration of specific radioactivityof 5% U-235

TABLE 14 (2) Precipitation test of sodium fluoride (NaF) afterprecipitation of sodium diuranate (NaDU) U F Order Test process (Bq/cc)(ppm) 1st NaDU-precipitation 0.006 1 supernatant + NH₄F 2ndNaDU-precipitation 0.011 1 supernatant + NH₄F

1) Test type: After a cylinder wastewater (nitric acid (HNO₃) was notadded) was treated using a compound including uranium (U), sodium (Na),and fluorine (F) to perform precipitation, the supernatant was subjectedto simple distillation to precipitate sodium fluoride (NaF), followed bysampling

2) Procedure: 300 ml of the wastewater→15 g of sodium hydroxide (NaOH)was added→filtration→250 ml of the filtrate+ammonium fluoride (NH₄F) (80ml)→the filtrate was subjected to simple distillation, followed bysampling→analysis of fluorine (F) and activity

Experimental Example 5

Experiment in device for recovering uranium (U) using a process fortreating washing wastewater released during a process of washing auranium hexafluoride (UF₆) cylinder according to the present invention

(1) First Experiment

1) Experimental Condition

(a) 30 kg of cylinder washing wastewater+1.5 kg of NaOH (aq, 30%)

(b) NaOH addition speed: 300 g/min

(c) Reaction time: 30 min

(d) Reaction temperature: 40 to 60° C.

(e) Reaction pressure: 0 bar·G

(f) Evaporation temperature: 110 to 130° C.

2) Object

(a) Measurement of the amounts of uranium (U) and fluorine (F) in eachstep under experimental conditions

TABLE 15 3) Experimental result Atomic energy licensing standardsClassifi- U F and environmental cation Sample content content regulationstandards 1 Cylinder washing  0.60% 2,557 ppm — wastewater 2 NaDUfiltrate 11 ppm 5,613 ppm Satisfied 3 NaDU cake 15.30% 4,603 ppm — 4Condensate 0.8 ppm    4 ppm Satisfied

4) Others

(a) Specific gravity of cylinder washing wastewater: 1.028

(2) Second Experiment

1) Experimental Conditions

(a) 20 kg of cylinder washing wastewater+1 kg of NaOH (aq, 30%)

(b) NaOH addition speed: 2 kg/min

(c) Reaction time: 30 min

(d) Reaction temperature: 40 to 60° C.

(e) Reaction pressure: 0 bar·G

(f) Evaporation temperature: 110 to 130° C.

2) Object

(a) Comparison of changes in the amounts of uranium (U) and fluorine (F)depending on the addition speed of sodium hydroxide (NaOH)

(b) Comparison of the first and second experiments after the amounts ofwashing wastewater and sodium hydroxide (NaOH) that were added in thefirst experiment are each reduced by ⅓ in order to reduce the amount ofwastewater released during the experiment

TABLE 16 3) Experimental result Atomic energy licensing standardsClassifi- U F and environmental cation Sample content content regulationstandards 1 Filtrate of  0.32% 1,507 ppm — cylinder washing wastewater 2NaDU filtrate 11 ppm 4,608 ppm Satisfied 3 NaDU cake 52.80% 2,665 ppm —4 Condensate 0.1    1 ppm Satisfied ppm (0.05 Bq/cc)

(3) Third Experiment

1) Experimental Conditions

(a) 20 kg of cylinder washing wastewater+2 kg of NaOH (aq, 30%)

(b) NaOH addition speed: 2 kg/min

(c) Reaction time: 30 min

(d) Reaction temperature: 40 to 60° C.

(e) Reaction pressure: 0 bar·G

(f) Settling (30 min) and bottom solution drain (1 Liter)

(g) Evaporation temperature: 110 to 130° C.

2) Object

(a) Comparison of the amount of the radioactivity of the condensate whenthe addition amount of sodium hydroxide (NaOH) is increased, with thatof other experiments

TABLE 17 3) Experimental result Atomic energy Amount of licensingstandards Classifi- radioactivity and environmental cation Sample(Bq/cc) regulation standards 1 Filtrate of cylinder 189.600 — washingwastewater 2 NaDU filtrate 0.425 Satisfied 3 Condensate N.D* (<0.03)Satisfied *Non-detected

(4) Fourth Experiment

1) Experimental Conditions

(a) 20 kg of cylinder washing wastewater+2 kg of NaOH (aq, 30%)

(b) NaOH addition speed: 2 kg/min

(c) Reaction time: 30 min

(d) Reaction temperature: 40 to 60° C.

(e) Reaction pressure: 2.5 bar·G

(f) Settling (30 min) and bottom solution drain (1 Liter)

(g) Evaporation temperature: 110 to 130° C.

2) Object

(a) Comparison of the amount of the radioactivity of the condensate whenthe reaction pressure is increased as high as possible with that ofother experiments

TABLE 18 3) Experimental result Atomic energy Amount of licensingstandards Classifi- radioactivity and environmental cation Sample(Bq/cc) regulation standards 1 Condensate (30 min 0.0224 Satisfied afterevaporation) 2 Condensate (60 min 0.0145 Satisfied after evaporation)

(5) Fifth Experiment

1) Experimental Conditions

(a) 20 kg of cylinder washing wastewater+2 kg of NaOH (aq, 30%)

(b) NaOH addition speed: 2 kg/min

(c) Reaction time: 30 min

(d) Reaction temperature: 40 to 60° C.

(e) Reaction pressure: 0 bar·G

(f) Settling (30 min) and bottom solution drain (1 Liter)

(g) Evaporation temperature: 110 to 130° C.

2) Object

(a) Comparison of the amount of the radioactivity of the condensate whena sodium diuranate (NaDU) solution is filtered, followed by evaporationof a filtrate, with that of other experiments

TABLE 19 3) Experimental result Atomic energy Amount of licensingstandards Classifi- radioactivity and environmental cation Sample(Bq/cc) regulation standards 1 Condensate (30 min 0.0195 Satisfied afterevaporation) 2 Condensate (60 min 0.0055 Satisfied after evaporation) 3Condensate 0.0466 Satisfied (evaporation of NaDU filtrate)

(6) Sixth Experiment

1) Experimental Conditions

(a) 20 kg of cylinder washing wastewater+1.5 kg of NaOH (aq, 30%)

(b) NaOH addition speed: 2 kg/min

(c) Reaction time: 30 min

(d) Reaction temperature: 40 to 60° C.

(e) Reaction pressure: 0 bar·G

(f) Settling (30 min) and bottom solution drain (1 Liter)

(g) Evaporation temperature: 110 to 130° C.

2) Object

(a) Comparison of the amount of the radioactivity of the condensate whenthe amount of sodium hydroxide (NaOH) that is added is reduced with thatof other experiments

3) Experimental Result

TABLE 20 Atomic energy Amount of licensing standards Classifi-radioactivity and environmental cation Sample (Bq/cc) regulationstandards 1 Condensate (30 min 0.0135 Satisfied after evaporation) 2Condensate (60 min 0.0322 Satisfied after evaporation)

Experimental Examples 1 to 4 of the present invention provide data onexperiments performed in order to improve the conventional process fortreating washing wastewater. Experimental Example 5 is an experiment forconfirming whether or not the process of the present invention satisfiesatomic energy licensing standards and environmental regulationstandards. FIG. 4 schematically shows an experimental apparatus.

In the present experiments, the addition amount and the addition speedof sodium hydroxide (NaOH), the reaction temperature and time, and thepH were selected as variables, and the results depending on thevariables were compared to each other. As for atomic energy licensingstandards and environmental regulation standards, the sodium diuranate(NaDU) filtrate can be transported from a radiation-controlled area to anon-controlled area when the content of uranium (U) is 20 ppm or less,and accordingly, the sodium diuranate filtrate may be transported to achemical treatment factory. The condensate can be released to theenvironment when the concentration of uranium (U) is 1 ppm or less(<0.08 Bq/cc) and the concentration of fluorine (F) is 10 ppm or less.Experiments were performed while the variables were changed in order toconfirm the regions in which the atomic energy licensing standards andenvironmental regulation standards were or were not satisfied. Allexperimental results satisfied atomic energy licensing standards andenvironmental regulation standards. Appropriate reaction conditions maybe selected according to the situation for operation of a commercialapparatus according to the present invention.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

Accordingly, the actual scope of the present invention will be definedby the appended claims and equivalents thereof.

1. A method of recovering uranium (U) using a process for treating awashing wastewater (hydrogen peroxide (H₂O₂)+sodium carbonate (Na₂CO₃)+auranium complex) released during a washing process of a uraniumhexafluoride (UF₆) cylinder, the method comprising: (1) adding sodiumhydroxide (NaOH) to the washing wastewater to precipitate the uraniumcomplex, contained in the washing wastewater, in a sodium diuranate(NaDU) form; (2) separating a sodium diuranate (NaDU) precipitate formedduring the step (1) and the washing wastewater using filtration; (3)evaporating the washing wastewater filtered during the step (2); and (4)cooling a vapor generated during the step (3) to recover a condensateand then checking remaining amounts of uranium (U) and fluorine (F). 2.The method of claim 1, wherein a demineralized water or a mixedsolution, including the hydrogen peroxide (H₂O₂) and the sodiumcarbonate (Na₂CO₃), is used as a washing solution during the washingprocess of the uranium hexafluoride (UF₆) cylinder, causing generationof the washing wastewater.
 3. The method of claim 1, further comprising:after the step (3), (5) filtering and evaporating a remaining wastewaterafter the evaporating of the step (3); and (6) cooling a vapor generatedduring the step (5) to recover a condensate and then checking remainingamounts of uranium (U) and fluorine (F).
 4. The method of claim 1,wherein a sodium hydroxide (NaOH) aqueous solution is added while thewashing wastewater is heated during the step (1) so that a pH iscontrolled to form a sodium diuranate (NaDU) solid, thereby performingprecipitation.
 5. The method of claim 1, wherein during the step (3), asteam is supplied to evaporate water, the evaporated water istransported through a heat exchanger to a condensate storage tank, and aresidue is returned to the step (2).
 6. A device for recovering uranium(U) using a process for treating a washing wastewater released during awashing process of a uranium hexafluoride (UF₆) cylinder, the devicecomprising: a NaDU reactor for adding sodium hydroxide (NaOH) to thewashing wastewater (hydrogen peroxide (H₂O₂)+sodium carbonate (Na₂CO₃)+auranium complex), released during the washing process of the uraniumhexafluoride (UF₆) cylinder, to thus precipitate a sodium diuranate(NaDU) solid; a filter separator connected to the NaDU reactor toseparate the sodium diuranate (NaDU) solid generated in the NaDU reactorand a filtrate; a filtrate reception tank connected to the filterseparator to store the filtrate separated using the filter separator; anevaporation vessel connected to the filtrate reception tank to evaporatethe filtrate supplied from the filtrate reception tank; a heat exchangerconnected to the evaporation vessel to cool a vapor obtained duringevaporation using the evaporation vessel, thus condensing the vapor; anda condensate storage tank connected to the heat exchanger to store acondensate.
 7. The device of claim 6, wherein another filter separatoris connected to the evaporation vessel to separate the sodium diuranate(NaDU) solid and the filtrate.
 8. The device of claim 6, wherein thecondensate storage tank includes a first condensate storage tank, forstoring a condensate to be released after amounts of radioactivity andfluorine (F) are checked, and a second condensate storage tank, forstoring a condensate that is to be chemically treated.